Valve gated injection molding apparatus is well known. Such apparatus utilizes a valve pin slidably received in a valve gate to control flow of melt when molding a part, to ensure a positive shut-off of the gate. While this technology has been utilized for decades in view of its positive shut-off attributes, it suffers from leakage problems upstream of the gate.
The valve stem moves slidably within a tight fitting bushing secured to a rear face of a nozzle housing. The nozzle housing provides a melt passage from a manifold to a nozzle tip mounted to the nozzle housing. The nozzle has a cap which tip registers with the gate. The valve pin extends through the bushing, through the melt passage and into a melt opening in the gate. The bushing supports the valve pin for its slidable movement and furthermore provides a seal to prevent melt from flowing out of the nozzle housing along the valve pin.
As one would expect, over a period of time, as the valve pin rubs against the bushing, wear will occur. Eventually the wear will create a significant gap between the valve pin and the bushing enabling melt to leak out between the two components, which may affect movement of the valve pin.
None of the present valve gated systems utilizing a valve pin bushing are maintenance friendly. Accordingly, replacement of the bushing generally requires removal and complete disassembly of the mold. Generally, the bushings are retained within the nozzle housing and accessible only upon removal of the nozzle housing which in turn requires removal of the portions of the mold in which the nozzle housing is mounted. At a minimum, a rear plate of the mold must be removed which in effect amounts to disassembly of the mold whether or not this is done in situ.
It is an object of the present invention to facilitate bushing removal for valve gate maintenance to enable replacement of such wear components without disassembly of the hot runner.